Four-stroke internal combustion engine with spark ignition

Abstract

In order to optimize combustion in a four-stroke spark-ignition engine with direct fuel injection, the conditions of charge flow are improved by providing the top surface of each piston with an essentially U-shaped guiding rib, which is open towards the exhaust side of the combustion chamber, fuel injection taking place into the concave area inside the guiding rib. The nozzle opening of the fuel injection device as well as the ignition source are positioned in the area of the cylinder center, i.e., preferably on different sides of the longitudinal center plane of the engine.

We claim: 
     
       1. A four-stroke internal combustion engine with spark ignition, comprising: an injection device located in a cylinder head for direct injection of a fuel into a combustion chamber, with a reciprocating piston per cylinder, and a roof-shaped combustion chamber top with two or more intake valves as well as intake ports generating a tumble flow in the combustion chamber and arranged on one side of a longitudinal center plane defined by a crankshaft axis and a cylinder axis, as well as an ignition source located in an area of a cylinder center, wherein the piston is provided on its top face next to the combustion chamber with a flow guiding rib which is essentially U-shaped in plan view, said "U" opening towards an exhaust side of the combustion chamber, and a top face of the piston assuming a continuously curved, concave shape between the guiding rib and an outer edge of the piston, and fuel injection taking place into a concave area inside the "U", and a nozzle opening of the fuel injection device being positioned in an area of the longitudinal center plane of the engine.   
     
     
       2. A four-stroke internal combustion engine as claimed in claim 1, wherein the piston top face is partly situated below a reference plane through the outer piston edge, i.e., on a crankshaft side of said plane. 
     
     
       3. A four-stroke internal combustion engine as claimed in claim 1, wherein the guiding rib is provided with a rounded upper edge, whose curved part smoothly joins with the concave top face of the piston. 
     
     
       4. A four-stroke internal combustion engine as claimed in claim 3, wherein the radius of the rounded part of the guiding rib amounts to 1 to 3 mm. 
     
     
       5. A four-stroke internal combustion engine as claimed in claim 3, wherein the radius of the rounded part of the guiding rib assumes its smallest value in an area of a cylinder center plane normal to the crankshaft axis. 
     
     
       6. A four-stroke internal combustion engine as claimed in claim 1, wherein the largest distance between guiding rib and longitudinal center plane, as measured normally to the longitudinal center plane, is at least 0.1 times the piston diameter, and at most 0.4 times the piston diameter, approximately. 
     
     
       7. A four-stroke internal combustion engine as claimed in claim 1, wherein the guiding rib has the greatest possible height, i.e., at least in parts, which height is defined by the contour of the roof of the combustion chamber when the piston is in upper dead center, and by the necessary clearance of the valves. 
     
     
       8. A four-stroke internal combustion engine as claimed in claim 7, wherein the region of the greatest height is in the area of the cylinder center plane normal to the crankshaft axis. 
     
     
       9. A four-stroke internal combustion engine as claimed in claim 1, wherein a nozzle opening of the injection device is located on an exhaust side, a radial distance from the cylinder axis being not more than about 0.2 times the piston diameter. 
     
     
       10. A four-stroke internal combustion engine as claimed in claim 1, wherein a symmetry axis of an injection jet produced by the injection device encloses an angle with the longitudinal center plane of not more than 30° and is directed towards the area of the cylinder center, as seen in the direction of the cylinder axis. 
     
     
       11. A four-stroke internal combustion engine as claimed in claim 1, wherein the conical injection jet produced by the injection device has a cone angle of at least 60° and at most 120°. 
     
     
       12. A four-stroke internal combustion engine as claimed in claim 11, wherein the conical injection jet produced by the injection device has a cone angle of 90°. 
     
     
       13. A four-stroke internal combustion engine as claimed in claim 1, wherein an ignition source is positioned on an intake side, a radial distance from the longitudinal center plane being at most 0.2 times the piston diameter. 
     
     
       14. A four-stroke internal combustion engine as claimed in claim 1, wherein the symmetry axes of an ignition source and an injection jet produced by the injection device enclose an angle of at least 60° and at most 120°, approximately. 
     
     
       15. A four-stroke internal combustion engine as claimed in claim 1, wherein the guiding rib, as seen in the direction of the cylinder axis, has a curvature radius of 0,2 to 0.6 times the piston diameter in the area of the cylinder center plane. 
     
     
       16. A four-stroke internal combustion engine as claimed in claim 1, wherein the guiding rib is positioned on the intake side, i.e., at least predominantly. 
     
     
       17. A four-stroke internal combustion engine as claimed in claim 1, wherein the ends of the guiding rib are approximately positioned in the area of the longitudinal center plane of the engine. 
     
     
       18. A four-stroke internal combustion engine as claimed in claim 1, wherein the guiding rib is symmetrical to the cylinder center plane.